As a conventional head-mounted type image display device, devices capable of mobile use such as head-set type devices and eyeglass type devices, for example, have been suggested (e.g. JP2003-502713A and JP2006-003879A).
FIG. 16 is a view showing a schematic structure of a conventionally proposed head-mounted type image display device, wherein FIG. 16(a) is a front view, FIG. 16(b) is a side view, and FIG. 16(c) is a plan view. This head-mounted type image display device 100 is of the type for left eye and has a head-set type head support unit 101, which is held on the left ear of an observer M, and a bar-like light guiding unit 104, which is connected to the head support unit 101 via an intermediate unit 102 and a supporting unit 103 so as to be held within the field of the left eye of the observer M. The bar-like light guiding unit 104 has an eyepiece optical unit 105 coupled to the end thereof opposite to the supporting unit 103. Moreover, a display element (not shown) such as liquid crystal display element and an organic electroluminescence display element, for displaying an image to be observed, is embedded in the head support unit 101, the intermediate unit 102 or the supporting unit 103, such that image light of an image displayed on the display element is emitted from the eyepiece optical unit 105 through the bar-like light guiding unit 104. The above-mentioned structure can be modified to reverse left and right for right eye use.
The head-mounted type image display device 100 shown in FIG. 16 is configured to allow the observer to observe an enlarged virtual image of an image displayed on the display element (not shown), by making the observer M see through the eyepiece optical unit 105 in a state where the head support unit 101 is supported on the left ear of the observer M such that the image light emitted from the eyepiece optical unit 105 is incident on the pupil of the observer M's left eye, that is, by making the visual axis of the left eye substantially coincide with the emitting optical axis of the eyepiece optical unit 105.
FIG. 17 is a perspective view showing a schematic structure of a conventionally proposed eyeglass-shaped head-mounted type image display device. This head-mounted type image display device 110 is integrated with an eyeglass, adapted for right eye use and has a bar-like light guiding unit 115, which is retained on the frame 111 of the eyeglass via a support unit 112 and a supporting unit 113 so as to be close to the front of the right eye glass lens 114 within a right eye field of an observer. The bar-like light guiding unit 115 has an eyepiece optical unit 116 coupled to the end thereof opposite to the supporting unit 113. Moreover, a display element (not shown) such as liquid crystal display element and a organic electroluminescence display element, for displaying an image to be observed, is installed in the eyeglass frame 111, support unit 112, or supporting unit 113 such that image light of an image displayed in the display element is emitted from the eyepiece optical unit 116 through the bar-like light guiding unit 115.
The head-mounted type image display device 110 shown in FIG. 17 is designed to make image light emitted from the eyepiece optical unit 116 be incident on the pupil of the observer's right eye through the right eye glass lens 114 when the observer wears the eyeglass frame 111. Thus, the observer can observe an enlarged virtual image of an image displayed on the display element (not shown), by wearing the eyeglass frame 111 and seeing through the eyepiece optical unit 116, that is, by bringing the visual axis of the right eye substantially in line with the emitting optical axis of the eyepiece optical unit 116.
In addition, as an eyeglass-shaped head-mounted type image display device, a device which is detachable to an ordinary eyeglass frame for use similar to the use of the head-mounted type image display device 110 shown in FIG. 17, has also been suggested.
There is a demand for information display that a lot of information should be displayed at the same time. However, the above-mentioned conventional head-mounted type image display device comprises only one eyepiece optical unit for emitting image light, and information is displayed on the single display screen of the single eyepiece optical unit. Besides, since the head-mounted type image display device has a relatively small display screen to allow mobile use thereof, the device can display only relatively little information. Particularly, in a case such as JP2006-003879A where a width of projection of a sectional shape in a direction of visual axis of an observer, of the eyepiece optical unit and the bar-like light guiding unit, is equal to or less than 4 mm so that the eyepiece optical unit and the bar-like light guiding unit allow the observer to have see-through vision, the display screen becomes further smaller and further less information can be displayed.
Therefore, the conventional head-mounted type image display device may not well satisfy a need to see a lot of information at the same time as in an information display.
A possible way to address such a need as described above is to provide a plurality of eyepiece optical units so that information is displayed by a multi-screen. However, simply providing a plurality of eyepiece optical units to display information by a multi-screen results in poor visibility of a display screen and deterioration of mobile-maneuverability due to juxtaposed or overlapped display images, different images being simultaneously observed by left and right eyes, respectively, and unnecessary image light being incident on the eyes, which are caused by the plurality of eyepiece optical units.